This invention relates to a well treatment problem of long standing; that of effectively contacting plugged fluid passageways between the borehole and reservoir with heat and oil solvent when those passageways are covered by a column of relatively dense brine.
The solid materials that plug such fluid passageways are usually heat-sensitive and oil-solvent-soluble materials, such as paraffinic and/or asphaltenic solids. But, it has previously been difficult, if not impossible, to contact brine-submerged plugged passageways with either a hot fluid, such as hot water or steam, or an oil solvent, such as an aromatic liquid. When either the hot fluid or oil solvent are piped into the borehole and discharged at a point lower than the plugged passageways they tend to flow upward, within the column of brine, and into the borehole annulus or to flow outward, through the passageways which are not plugged, and into the reservoir, in a manner providing little or no contacting or heating of the plugged passageways.
U.S. patents such as the following have suggested numerous procedures for unplugging such brine-submerged passageways. U.S. Pat. No. 2,228,629 suggests dropping into a well borehole a silk or wool container filled with oil-coated particles of aluminum and flaked caustic soda, so that those materials will react when the fabric container is ruptured within the brine in the borehole. U.S. Pat. No. 2,799,342 suggests injecting an oil solvent dispersion of alkali metal particles (smaller than about 5 microns) into an aqueous liquid within the borehole. U.S. Pat. No. 2,889,884 suggests injecting into the reservoir a non-aqueous solvent solution of metal hydrides which are exothermically reactive with water. U.S. Pat. No. 3,279,514 suggests separately injecting fluids containing an oil solvent, water, and a liquid dispersion of a salt or hydroxide which reacts exothermically with water, so that the fluids mix and react. U.S. Pat. Nos. 3,342,264 and 3,342,265 suggest sequentially injecting compositions containing triglyceride oils (such as lecithin) and aqueous alkali, and then flushing the boreholes with water to remove such passageway plugging materials. U.S. Pat. No. 3,914,132 suggests injecting a solvent mixture of aromatic hydrocarbon and amine as an oil solvent which is capable of dissolving any contacted asphaltenic solids.
In the course of research relating to other well treating problems, it has been found that certain self-reactive aqueous solutions could be compounded and flowed into wells with their components arranged to subsequently react to yield nitrogen gas and heat at times and rates which were useful for various well treating processes. Such discoveries have been described in the following U.S. patents and patent applications.
U.S. Pat. No. 4,178,993 by E. A. Richardson and R. F. Scheuerman describes a process for initiating fluid production from a liquid-containing well by injecting an aqueous solution containing nitrogen-gas-generating reactants having a concentration and rate of reaction correlated with the pressure and volume properties of the reservoir and the well conduits to react at a moderate rate within the well and/or the reservoir to generate enough gas to displace sufficient liquid from the well to reduce the hydrostatic pressure within the well to less than the fluid pressure within the reservoir.
U.S. Pat. No. 4,219,083 by E. A. Richardson and R. F. Scheuerman describes a process for cleaning well casing perforations by injecting an aqueous solution containing nitrogen-gas-generating reactants, an alkaline buffer providing a reaction-retarding pH and an acid-yielding reactant for subsequently overriding the buffer and lowering the pH in order to trigger a fast-rising pulse of heat and pressure which causes a perforation-cleaning backsurge of fluid through the perforations.
U.S. Pat. No. 4,232,741 by E. A. Richardson, R. F. Scheuerman, D. C. Berkshire, J. Reisberg and J. H. Lybarger describes a process for temporarily plugging thief zones within a reservoir by injecting an aqueous solution containing nitrogen-gas-generating reactants, a foaming surfactant, an alkaline buffer and an acid-yielding reactant, arranged so that they initially delay the reaction and subsequently initiate a moderate rate of gas production, in order to form a foam which is, temporarily, relatively immobile within the reservoir formation.
Patent application Ser. No. 127,355 filed Mar. 5, 1980, by D. R. Davies and E. A. Richardson describes a process for conducting a production test by circulating a solution of nitrogen-gas-generating reactants within conduits within a well, with the solution buffered at a pH providing a promptly-initiated reaction having a relatively mild rate and being inflowed through a well conduit at a rate such that the gas being generated serves as a lift-gas for gas-lifting fluid from the reservoir through another well conduit.
Patent application Ser. No. 215,895 filed Dec. 12, 1980, by E. A. Richardson and W. B. Fair, Jr. now U.S. Pat. No. 4,330,037 describes a process for treating an oil-containing reservoir in order to concurrently chemically heat the reservoir and increase its effective permeability to oil by injecting an aqueous solution of nitrogen gas-generating reactants which is arranged to have a volume, a rate of reaction and a heat-generating capability such that the heat-generation will occur below a selected depth and will cause a selected volume of the reservoir to be heated to a selected temperature.
The disclosures of the U.S. Pat. Nos. 4,178,933; 4,219,083 and 4,232,741 and the patent applications Ser. Nos. 127,355 and 215,895 are incorporated herein by cross-reference.